1. Field of the Invention
The present invention relates to preparation of polychlorinated pyridine mixtures by direct liquid phase chlorination of alpha-picoline. Typical of the products produced are 3-chloro; 6-chloro; 5,6-dichloro; 3,6-dichloro; 3,5-dichloro; 3,5,6-trichloro; 3,4,5-trichloro and 3,4,5,6-tetrachloro-2-trichloromethyl pyridine. These products have utility as herbicides, pesticides, nitrification inhibitors, and intermediates for herbicides and insecticides.
2. Description of the Prior Art
Compositions enriched in 6-chloro-2-trichloromethyl pyridine have highly useful properties in agriculture applications, particularly in improving agricultural soil by retarding oxidation of ammonia ions in soil thereby improving plant nutrition therein, as described in Goring U.S. Pat. No. 3,135,594. Mixtures containing significant amounts of 3,6-dichloro, 3,5-dichloro and 5,6-dichloro-2-trichloromethyl pyridine, as produced by the present invention have proven useful as raw materials in the production of 2,3,5,6-tetrachloro pyridine and 2,3,4,5,6-pentachloro pyridine which also have utility as herbicides and pesticides and are also employed as chemical intermediates in the preparation of other herbicides and pesticides, such as those described in Dietsche et al U.S. Pat. No. 4,256,894.
Mixtures containing significant quantities of 3-chloro-2-trichloromethyl pyridine, which are also produceable by the process of the present invention, have utility as intermediates for preparation of herbicide compositions such as described in Johnston et al U.S. Pat. No. 3,317,549. 3,4,5-trichloro-2-trichloromethyl pyridine may be chlorinated further to useful products as described in Johnston et al U.S. Pat. No. 3,186,994 and Johnston et al U.S. Pat. No. 3,418,323, and mixtures containing high yields of 3,4,5-trichloro-2-trichloromethyl pyridine and 3,4,5-trichloro-2-dichloromethyl pyridine are also readily obtainable by the process of the present invention, it being further notable in this regard that the 3,4,5-trichloro-2-dichloromethyl pyridine constituent of such mixtures is easily convertible to 3,4,5-trichloro-2-trichloromethyl pyridine by the process disclosed in Johnston et al U.S. Pat. No. 3,173,919.
Previous methods for preparing mixtures rich in 6-chloro-2-trichloromethyl pyridine are described in Taplin U.S. Pat. No. 3,424,754 and Taplin U.S. Pat. No. 3,420,833. In the examples of U.S. Pat. No. 3,424,754 yields of about 75% volatiles of mixtures containing about 90% 6-chloro-2-trichloromethyl pyridine (providing a net yield of about 68% by weight of 6-chloro-2-trichloromethyl pyridine) are obtained by chlorinating preformed alpha-picoline hydrochloride fed into the vapor space above an initiator charge at a temperature of 220.degree. C. An essential function of the initiator charge is to react with chlorine and generate HCl which is combined with the alpha-picoline in another vessel to form liquid picoline hydrochloride. The production of mixtures rich in 6-chloro-2-trichloromethyl pyridine by reacting alpha-picoline vapor with chlorine in the vapor phase at temperatures in excess of 400.degree. C. with an inert diluent present are described in Taplin U.S. Pat. No. 3,420,833. This is an energy intensive process because all feeds and diluents must be vaporized. Johnston et al U.S. Pat. No. 3,418,323 describes a method of preparing 6-chloro-2-trichloromethyl pyridine by reacting chlorine with 2-trichloromethyl pyridine in the liquid phase at temperatures from 120.degree. C. to 135.degree. C. in the presence of ultraviolet light. In the past, successful direct chlorination of alpha-picoline has been limited to reaction thereof in the vapor phase as in Taplin U.S. Pat. No. 3,420,833. Direct feed of alpha-picoline into a liquid phase chlorination reactor is not practical according to the teaching of Taplin U.S. Pat. No. 3,424,754 (at page 3, lines 34-41), and Norton et al U.S. Pat. No. 3,256,167 (at page 3, lines 34-40). These prior art teachings indicate that intractable mixtures result. In marked contrast to such teachings, practice of the present invention, involving direct feed of alpha-picoline to a liquid phase reaction mass, produces fluid and tractable mixtures containing high yields of polychlorinated picolines.